A continuous flow, tube viscosimeter is described which permits determination of viscosities and gel strengths of abrasive thixotropic fluids at temperatures up to 250°F. Provision is made for the introduction of treating chemicals into the closed system, while under pressure, without interrupting fluid flow. The new instrument employs a special rubber tube pump which maintains constant flow under various pressures and is unaffected by abrasive materials. Flow characteristics of the pump are discussed, and tube and Stormer viscosimeter data are compared.